|Origin:||maniacus, from Greek maniakos, from mania; MANIA|
someone who behaves in a stupid or dangerous way [= lunatic]:
He drove like a maniac to the hospital.
Suddenly this maniac ran out into the middle of the road.
someone who you think is too involved or interested in religion or sex [= freak]:
The woman's a sex maniac if you ask me.
someone who is mentally ill
homicidal maniac (=one who kills people)